I don't use home warranties, but do have maintenance contracts with our local HVAC and plumbing companies that I use for repairs too - both maintenance contracts give me a greater discount if something needs repair or replacement and includes two annual service calls for maintenance. On the plumbing contract I don't pay for someone to go out to the property if there is a problem, so save the service call fee ($50) anytime I need it in the year, plus the contract includes one maintenance call in the year to check the plumbing and appliances ($100) and if I need work done (hasn't happened yet, thankfully) it's discounted 20% off their rates charged to those without a contract - that costs $65 for the year. The HVAC contract also has no charge for calls out to the houses ($50), includes two service calls a year for maintenance (winter/summer change overs, filters, line checks, etc) ($100) and a discount on work if needed, I think that's 15% off standard rates for those without a contract. That one costs $89 a year and includes all the things needed for the maintenance calls (ie. filters, etc.).
I think they're worth it, especially the HVAC since they remember when to change filters and schedule that to be done twice a year - and since both include service calls at no charge to go out and figure out what's wrong, that alone pays for the contract in a year since we do wind up with a couple of calls a year for something, usually nothing, but something none the less to appease a tenant.